Scanning Imaging Devices provide an exemplary indication of image distortion problems, and they cover a broad range of systems that all could have similar problems. Such problems may result in image distortion resulting from error introduction relating to a difference between a desired location of image capture and an actual location during scanning. A number of scanning and non-scanning imaging devices may be affected and can include Electron Beam systems, Focused Ion Beam systems, Laser Imaging systems, scanning electron microscopes (SEM), transmission electron microscopes (TEM), and optical systems. Scanning systems are characterized in that the image capture mechanism is scanned over the target substrate and image data collection is collected during such scan. Non-scanning systems may make one or more image data collections of a substrate. In either case, a discrepancy between the desired location of image data collection and the actual location may result in distortion in the resulting image.
When a signal indicative of characteristics of a portion of substrate to be imaged, e.g. a surface or a cross-section of a substrate, is collected, there is often a small degree of error introduced between the actual location being analyzed on the substrate with the intended location being analyzed. The location of analysis on the substrate is related to at least the current relative position and/or relative orientation of one or all of the beam emitter, the emitted beam, the signal detector, and the substrate. The actual location of analysis may often be different from the intended location for analysis, which causes distortion when assessing characteristics of the surface or cross section, including for example when the applicable signal analysis values are assembled together to form an image. The difference between actual and intended locations may be introduced from a complex variety of sources, and interaction thereof, relating to the imaging device.
There are a variety of sources of error which may contribute to differences between the intended and actual location on the substrate for analysis. These errors may be introduced by such factors as unexpected electromagnetic field values, mechanical and control system imperfections, lens imperfections, environmental changes, scanning rates (in the case of a scanning imaging device), among myriad other factors, as well as the interactions therebetween. These and other factors introduce an offset between the intended and actual locations for data collection on the substrate being imaged, where such presumed location may be based on a number of factors, including the relative location and position of the beam emitter, the beam, the signal detector, and the substrate itself. Due to the number of sources of error, the interaction therebetween, and the complexity of accounting for all such errors in determining the actual location of sample measurement in different measurements at different times, accounting for such errors in generating an image has been difficult in all circumstances, particularly at higher resolutions and/or for larger regions. Moreover, when mosaicking such images to form a larger image, or aligning such images, mosaicked or otherwise, vertically (e.g. 3-D models), the image distortion can introduce additional uncertainties.
Another source of error for scanning image data collectors may result from differences in the relative size of the substrate capture region to the corresponding image region, as well as inconsistencies of such differences over the substrate. This may result in, for example, changes in the rate of travel of the scanning infrastructure relative to the sampling rate. As such, a sample acquired at a first location may correspond to a particular area of the surface or cross-section, which may then be used for generating image data corresponding to a pixel at that location, but due to differences in the aforementioned error at different locations on the substrate, the area at another location may be different.
This background information is provided to reveal information believed by the applicant to be of possible relevance. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art.